Question

aim: date: aim

1. factor #3 - mineral composition:

rocks weather at different rates depending upon mineral composition.

• rocks composed of harder, more resistant minerals will weather away more slowly
• rocks composed of softer, less resistant minerals will weather away more rapidly
• use page #16 of the esrt to find the hardness of the following minerals:

o muscovite mica: hardness =
o garnet: hardness =
o which mineral is the most resistant to weathering?
/ checkpoint:

1. identify each of the rock layers below. which layer is least resistant to weathering? which layer is most resistant to weathering?

a =
b =
c =
d =

1. which layer is the most resistant to weathering?
2. which layer is the least resistant to weathering?

the cross - section below represents an outcrop of sedimentary rock layers exposed on the earths surface. rock layers a, b, c, and d are labeled.

1. which rock layer shows the greatest resistance to weathering and erosion?
2. which rock layer shows the least resistance to weathering and erosion?

Explanation:

Step1: Find hardness from reference

According to the Mohs hardness scale (usually found on page 16 of ESRT - Earth Science Reference Tables), Muscovite Mica has a hardness of 2 - 2.5.

Step2: Find hardness of Garnet

Garnet has a hardness of 6.5 - 7.5 on the Mohs hardness scale.

Step3: Determine most resistant mineral

Generally, the harder the mineral, the more resistant it is to weathering. Since Garnet has a higher hardness range compared to Muscovite Mica, Garnet is more resistant to weathering.

Step4: Analyze rock - layer resistance

Without specific information about the rock - layer compositions in the diagrams, we assume that the more compact and less porous the rock, the more resistant it is to weathering. Usually, harder rocks (composed of harder minerals) are more resistant. In a typical sedimentary rock sequence, well - cemented and dense rocks are more resistant.

Answer:

Muscovite Mica hardness: 2 - 2.5
Garnet hardness: 6.5 - 7.5
Most resistant mineral to weathering: Garnet
(Answers for rock - layer questions require more information about the rock types in the diagrams, but in general, the harder and more compact the rock, the more resistant it is to weathering)